Intravascular arterial to venous anastomosis and tissue welding catheter

ABSTRACT

A device for creating an arteriovenous (AV) fistula includes a proximal base having a distal tapered end surface and a distal tip connected to the proximal base and movable relative to the proximal base. The distal tip has a proximal tapered end surface. A first heating assembly, including an energized heating element, is disposed on at least one of the distal tapered end surface and the proximal tapered end surface. A second heating assembly, comprising a passive non-energized heat spreader, is disposed on the other one of the distal tapered end surface and the proximal tapered end surface. The distal tapered end surface and the proximal tapered end surface are adapted to contact opposing sides of a tissue portion to create the fistula. The taper of the proximal tapered end surface matches the taper of the distal tapered end surface, so that the two surfaces match one another.

This application is a continuation under 35 U.S.C. 120 of commonlyassigned U.S. application Ser. No. 15/254,754, filed on Sep. 1, 2016 andentitled Intravascular Arterial to Venous Anastomosis and Tissue WeldingCatheter, now issued as U.S. Pat. No. 10,722,285, which in turn is adivisional under 35 U.S.C. 120 of commonly assigned U.S. applicationSer. No. 14/080,702, filed on Nov. 14, 2013 and entitled IntravascularArterial to Venous Anastomosis and Tissue Welding Catheter, now U.S.Pat. No. 9,439,710, which in turn claims the benefit under 35 U.S.C.119(e) of the filing date of Provisional U.S. Application Ser. No.61/726,544, entitled Intravascular Arterial to Venous Anastomosis andTissue Welding Catheter, filed on Nov. 14, 2012. Each of the foregoingapplications are herein expressly incorporated herein by reference, intheir entirety.

This application is related to U.S. application Ser. No. 13/161,356,entitled Intravascular Arterial to Venous Anastomosis and Tissue WeldingCatheter, filed on Jun. 15, 2011, to U.S. Provisional Application Ser.No. 61/596,670, entitled Intravascular Arterial to Venous Anastomosisand Tissue Welding Catheter, filed on Feb. 8, 2012, and to U.S.application Ser. No. 13/668,190, entitled Systems and Methods forPercutaneous Intravascular Access and Guidewire Placement, filed on Nov.2, 2012. Each of these applications are also each expressly incorporatedherein by reference, in their entirety.

BACKGROUND OF THE INVENTION

In the body, various fluids are transported through conduits throughoutthe organism to perform various essential functions. Blood vessels,arteries, veins, and capillaries carry blood throughout the body,carrying nutrients and waste products to different organs and tissuesfor processing. Bile ducts carry bile from the liver to the duodenum.Ureters carry urine from the kidneys to the bladder. The intestinescarry nutrients and waste products from the mouth to the anus.

In medical practice, there is often a need to connect conduits to oneanother or to a replacement conduit to treat disease or dysfunction ofthe existing conduits. The connection created between conduits is calledan anastomosis.

In blood vessels, anastomoses are made between veins and arteries,arteries and arteries, or veins and veins. The purpose of theseconnections is to create either a high flow connection, or fistula,between an artery and a vein, or to carry blood around an obstruction ina replacement conduit, or bypass. The conduit for a bypass is a vein,artery, or prosthetic graft.

An anastomosis is created during surgery by bringing two vessels or aconduit into direct contact. The vessels are joined together with sutureor clips. The anastomosis can be end-to-end, end-to-side, orside-to-side. In blood vessels, the anastomosis is elliptical in shapeand is most commonly sewn by hand with a continuous suture. Othermethods for anastomosis creation have been used including carbon dioxidelaser, and a number of methods using various connecting prosthesis,clips, and stents.

An arterio-venous fistula (AVF) is created by connecting an artery to avein. This type of connection is used for hemodialysis, to increaseexercise tolerance, to keep an artery or vein open, or to providereliable access for chemotherapy.

An alternative is to connect a prosthetic graft from an artery to a veinfor the same purpose of creating a high flow connection between arteryand vein. This is called an arterio-venous graft, and requires twoanastomoses. One is between artery and graft, and the second is betweengraft and vein.

A bypass is similar to an arteriovenous graft. To bypass an obstruction,two anastomoses and a conduit are required. A proximal anastomosis iscreated from a blood vessel to a conduit. The conduit extends around theobstruction, and a second distal anastomosis is created between theconduit and vessel beyond the obstruction.

As noted above, in current medical practice, it is desirable to connectarteries to veins to create a fistula for the purpose of hemodialysis.The process of hemodialysis requires the removal of blood from the bodyat a rapid rate, passing the blood through a dialysis machine, andreturning the blood to the body. The access to the blood circulation isachieved with (1) catheters placed in large veins, (2) prosthetic graftsattached to an artery and a vein, or (3) a fistula where an artery isattached directly to the vein.

Hemodialysis is required by patients with kidney failure. A fistulausing native blood vessels is one way to create high blood flow. Thefistula provides a high flow of blood that can be withdrawn from thebody into a dialysis machine to remove waste products and then returnedto the body. The blood is withdrawn through a large access needle nearthe artery and returned to the fistula through a second large returnneedle. These fistulas are typically created in the forearm, upper arm,less frequently in the thigh, and in rare cases, elsewhere in the body.It is important that the fistula be able to achieve a flow rate of 500ml per minute or greater, in order for the vein to mature or grow. Thevein is considered mature once it reaches >4 mm and can be accessed witha large needle. The segment of vein in which the fistula is createdneeds to be long enough (>6 cm) to allow adequate separation of theaccess and return needle to prevent recirculation of dialysed andnon-dialysed blood between the needles inserted in the fistula.

Fistulas are created in anesthetized patients by carefully dissecting anartery and vein from their surrounding tissue, and sewing the vesselstogether with fine suture or clips. The connection thus created is ananastomosis. It is highly desirable to be able to make the anastomosisquickly, reliably, with less dissection, and with less pain. It isimportant that the anastomosis is the correct size, is smooth, and thatthe artery and vein are not twisted.

SUMMARY OF THE INVENTION

The present invention comprises a device for creating an arteriovenous(AV) fistula, which comprises a proximal base having a distal taperedend surface and a distal tip connected to the proximal base and movablerelative to the proximal base. The distal tip has a proximal tapered endsurface. A first heating assembly, comprising an energized heatingelement, is disposed on at least one of the distal tapered end surfaceand the proximal tapered end surface. A second heating assembly,comprising a passive non-energized heat spreader, is disposed on theother one of the distal tapered end surface and the proximal tapered endsurface. The distal tapered end surface and the proximal tapered endsurface are adapted to contact opposing sides of a tissue portion tocreate the fistula. The distal tapered end surface is oriented at anangle of 15-90 degrees relative to a longitudinal axis of the device,and more advantageously at an angle of 15-50 degrees relative to thelongitudinal axis. In one particularly optimal configuration, the distaltapered end surface is oriented at an angle of approximately 23 degreesrelative to the longitudinal axis. The taper of the proximal tapered endsurface matches the taper of the distal tapered end surface, so that thetwo surfaces match one another and fully engage with one another whenengaged.

A shaft is provided for connecting the distal tip to the proximal base,the shaft being extendable and retractable to extend and retract thedistal tip relative to the proximal base.

The tapered end surface on which the heating assembly is disposedpreferably has a second passive non-energized heat spreader disposedthereon. The energized heating element optimally comprises a serpentineconfiguration. A temperature sensor is disposed near the energizedheating element, for providing closed loop temperature control to theheating assembly.

The second heat spreader comprises a thermally conductive material whichextends across a substantial portion of the tapered end surface on whichit is disposed, the second heat spreader being in thermal contact withthe energized heating element to draw heat from the heating element andspread the heat across the tapered end surface. It is constructed sothat it has a thickness approximately equal to a thickness of a vesselin which the device is deployed, this thickness falling within a rangeof 0.010 inches to 0.060 inches.

In one configuration, the heat spreader comprises a plurality of raisedsegments forming a segmented rib, for creating a focused heat conductionpath through tissue. The segmented rib further comprises gaps betweenthe segments, which gaps provide an insulative barrier that limitstissue dessication to promote adhesion without cutting. In anotherconfiguration, the heat spreader comprises a raised outer rib along itscircumference, the raised outer rib forming a pocket in a center portionthereof for capturing and removing tissue removed. An outercircumference of the rib comprises a radius for creating a transitionbetween a weld band outside of a cut zone formed during a procedure andnative tissue.

In other embodiments, the heat spreader comprises a domed surface, orcomprises a raised center surface and a lower profile outer surface.

The distal tip comprises a tapered outer surface, tapering down from theproximal tapered end surface toward a distal end thereof, the distal endof the distal tip comprising an aperture for a through lumen forreceiving a guidewire, wherein a width of the distal tip at the lumenaperture is approximately equal to a diameter of a guidewire.

The energized heating element comprises separate elliptical elementsthat provide independent power delivery for heating and cutting. Theseparate elliptical elements comprise an outer element and an innerelement, the outer element being configured to deliver reduced heat topromote controlled dessication and adhesion in a weld zone withoutcutting through tissue and the inner element being configured to deliverincreased heat to promote rapid cutting through tissue in a cuttingzone.

In illustrated embodiments, the first heating assembly is disposed onthe distal tapered end surface and the second heating assembly isdisposed on the proximal tapered end surface.

A second active energized heating element is provided on the proximaltapered end surface in some embodiments, which is embedded into the heatspreader.

Each of the first and second heating assemblies preferably comprisenon-stick surfaces, and the shaft also preferably comprises a non-sticksurface. The non-stick surfaces have a surface finish of less than 16Ra.

A position sensor is provided for monitoring movement of the distal tip.

In another aspect of the invention, there is provided a method forcreating an arteriovenous (AV) fistula, which comprises steps ofselecting an appropriate procedural site having each of a primary bloodvessel and a secondary blood vessel in close proximity to one another,inserting a piercing device into the primary vessel to pierce the vesselwalls and creating an opening so that the piercing device extends intothe adjacent secondary vessel, and advancing a guidewire until theguidewire is positioned in a blood flow path of the secondary vesselsufficiently to allow the piercing device to be removed. The piercingdevice is then withdrawn. A proximal end of the guidewire is loaded intoa lumen of a distal tip of a device for creating the AV fistula, and thedevice is advanced over the guidewire until a tapered dilating distaltip of the device comes into contact with the selected anastomosis site.The distal tip of the device is advanced relative to a proximal base ofthe device to thereby dilate the opening in the second vessel, so thatthe distal tip is in the second vessel and the proximal base is in thefirst vessel.

At this juncture, a heat spreader on an angled distal surface of theproximal base is seated against an inner wall of the first vesselsurrounding the opening. The distal tip is retracted so that a heatspreader on an angled proximal surface of the distal tip seats againstan inner wall of the second vessel surrounding the opening, therebycapturing the walls of the first and second vessel between the facingangled surfaces of each of the distal tip and the proximal base,respectively.

A controlled tension is maintained between the distal tip and theproximal base, and at the same time energy is applied to a heatingelement on the distal angled surface of the proximal base. The resultantapplied heat and pressure forms a fistula with welded edges defining thefistula opening. The device is then withdrawn from the procedural site.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin conjunction with the accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is an elevational view of the handle portion of a deviceconstructed in accordance with one embodiment of the present invention;

FIG. 1b is an elevational enlarged view of the circled distal workingportion of the device of FIG. 1 a;

FIG. 2a is an elevational view of an embodiment like that shown in FIGS.1a-1b , with the distal end in a first working configuration;

FIG. 2b is an elevational view similar to FIG. 2a , with the distal endin a second working configuration;

FIG. 3a is an isometric view of one embodiment of the device shown inFIGS. 1a -2 b;

FIG. 3b is an isometric view similar to FIG. 3a illustrating a modifiedembodiment of the heating mechanism;

FIG. 4a is an exploded isometric view illustrating an embodiment of theproximal base and particularly showing the assembly of the heatingelement and proximal heat spreader;

FIG. 4b is an isometric view showing the assembled heating element andproximal heat spreader;

FIG. 4c is an exploded isometric view similar to FIG. 4a showing amodified embodiment of the proximal heating assembly;

FIG. 5 is an exploded isometric view of another embodiment of theproximal base and heating assembly;

FIG. 6 is an exploded isometric view of an embodiment of the distal tipand distal heat spreader;

FIG. 7a is an isometric view of one embodiment of the distal tip andheating assembly of the present invention;

FIG. 7b is an isometric view similar to FIG. 7a of a modified embodimentof the distal tip and heating assembly of the present invention;

FIG. 7c is an isometric view similar to FIGS. 7a-7b of still anothermodified embodiment of the distal tip and heating assembly of thepresent invention;

FIG. 8a is an isometric view similar to FIGS. 7a-7c of yet anothermodified embodiment of the distal tip and heating assembly of thepresent invention;

FIGS. 8b-8f are cross-sectional views of different embodiments of thedistal tip and heating assembly of the present invention;

FIG. 9 is a cross-sectional view showing an application and method ofusing the device and system of the present invention;

FIG. 10 is a diagram of an anastomosis creating using the devices andmethods disclosed in the present application;

FIG. 11a is an elevational view similar to FIG. 1a illustrating amodified embodiment of the device of FIG. 1a , but having an activedistal heater rather than a passive heat spreader; and

FIG. 11b is an elevational enlarged view of the circled portion of FIG.11 a.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, as illustrated in FIGS.1a and 1b , one embodiment of the inventive intraluminal anastomoticdevice 1 comprises four main components, including a proximal heatingassembly 2, a proximal shaft 3, a distal heating assembly 4, and ahandpiece 6. The distal heating assembly 4 comprises a distal tip 5 andheat spreader 24. The handpiece 6 comprises a tip actuation button 7 anda release button 13. The proximal heating assembly 2 is constructed of aproximal base 10 that is cut at an angle θ at the distal end. In oneembodiment, the proximal base 10 is cut at an angle θ of 23 degrees,forming an angled distal tapered end surface 10 a. However, the angle θcan be adjusted depending on the particular anatomy of a procedural siteand desired anastomosis length. The inventors have found that the angleθ provides advantageous outcomes within a range of about 15-90 degrees,and more particularly within a range of 15-50 degrees, keeping in mindthat approximately 23 degrees is presently a particularly preferredangle within that range. These preferred angles/angle ranges result inan optimized oval configuration for the anastomosis which maximizes thecutting surface while also efficiently utilizing available heatingenergy to create an effective cut and welding zone.

On the angled surface 10 a of the proximal base 10, a heating element 8is embedded. The proximal base 10 is typically constructed of athermally insulating material that is resistive to high temperatures.Materials known to work well for this application include Vespel,Celazol, Teflon, Polyimide, Ultem, and ceramics. A proximal heatspreader 12 is used to compress and heat the tissue to create coaptationof vessel tissues. This process is known as tissue welding or tissuefusion. In one embodiment, the proximal heat spreader 12 is constructedof a thermally conductive material with the resistive heating elementembedded therein. Some examples of thermally conductive materialsuitable for this purpose include aluminum, stainless steel, aluminumnitride, or other metal or ceramic materials known to those skilled inthe art. The position, size, and shape of the proximal heat spreader 12can be adjusted to control where the heat is applied to tissue (seeFIGS. 3a and 3b for exemplary alternative embodiments). For example, itmay be beneficial to place the proximal heat spreader 12 toward thecenter of the long axis of the device body (FIG. 3b ), such that a heatgradient is created across the face of the angled surface of theproximal base 10. This provides the tissue near the center of thecutting region with the most heat, which completely denatures thetissue, and less heat radially outwardly of the center, to limit theamount of necrosis, while still providing strong coaptation or weldingof the tissues. The proximal base 10 is configured with at least onethermocouple or temperature sensor 14 to monitor the temperature nearthe active heating element 8, and provides a means for closed looptemperature control to optimize tissue welding and cutting.

As illustrated particularly in FIGS. 6 and 7 a-7 c, the distal tip 5comprises a uniform conical tapered outer surface, though it can have avariable tapered, sloped outer surface as illustrated in FIGS. 8a-8f ,wherein the outer surface tapers down to the approximate diameter of aguidewire to provide an atraumatic method for passing through the vesselwall. A guidewire lumen 18 extends through the center of the distal tip5, as shown in FIGS. 3a and 3b . In one particular embodiment, the lumen18 is sized to receive a 0.014 inch guidewire, but may be sized toreceive guidewires of various diameters. The intraluminal anastomoticdevice 1 is tracked over a guidewire 17 (FIG. 9) and the tapered outersurface of the distal tip 5 dilates through the tissue into the adjacentvessel. Once the distal heating assembly 4 is completely disposed withinthe adjacent vessel, the distal tip 5 is retracted to bring the tiptoward the proximal heating assembly 2, thereby capturing vessel walltissue between the two components 5 and 10, and bringing the adjacentwalls of a first vessel 20 and a second vessel 22 together. A proximalend surface 5 a of the distal heating assembly 4 is angled to preciselymatch the angle θ of the proximal heating assembly 2.

In one embodiment, the proximal base 10 is configured as shown in FIGS.3a and 3b . The proximal base 10 is configured to receive the firstheating element 8 (FIGS. 4a-4c ), which is covered by the proximal heatspreader or heating surface 12. The heating surface 12 is comprised of athermally conductive material which draws heat from the first heatingelement 8. Power attachment points 11 ensure that the heating element 8,in whichever illustrated configuration is selected, may be energized.The heating surface 12 transfers heat into the adjoining vessels tocreate a weld band 21 (FIGS. 9 and 10) and to cut tissue to create ananastomosis or fistula 25 (FIGS. 9 and 10). The size and shape of theweld zone and anastomosis can be altered by adjusting the shape of theheating surface 12. The geometry can also be altered such that thetemperature is equal in the passive and active heated surfaces. In onepreferred embodiment, the heating surface or proximal heat spreader 12comprises an aluminum plate, although alternative thermally conductivematerials such as aluminum nitride, ceramics, tungsten, steel, orberyllium may be used. The thickness of the heating surface 12 isapproximately the thickness of the vessel in which the weld is beingcreated. However, the thickness may be increased or decreased to controlthe amount of heat that is conducted into the surrounding tissue.Typical thickness of the heating surface ranges from 0.010 inches to0.060 inches (FIGS. 3a-3b, 4a-4c ).

In one embodiment as illustrated in FIG. 7b , a distal heat spreader 24on the distal tip 5 has a plurality of raised segments 29 for forming asegmented rib 30. The segmented rib 30 creates a focused heat conductionpath through the tissue, while gaps 31 between the segments 29 providean insulative barrier that limits tissue dessication to promote adhesionwithout cutting. The size and number of segments 29 can be adjusted tocontrol the rate of tissue dessication that may accommodate variabletissue thickness.

In another embodiment, as illustrated in FIGS. 7a and 8c , the passiveheating element 24 has a raised outer rib 28 along its circumference.The raised outer rib 28 creates a pocket 26 in the center where tissueis captured and removed during the welding process. The outercircumference of the rib has a radius to create a transition between theweld band outside of the cut zone and the native tissue. A radius allowsfor minimal compression at the edge of the weld. This configurationprovides a focused heat conduction path through the tissue between theactive and passive heating assemblies to promote tissue cutting whilethe step gap provides an offset that limits tissue compression anddessication in the inner and outer regions to promote tissue adhesionwithout cutting in the adjacent zone.

In still another embodiment as illustrated in FIG. 8f , the distalheating assembly 4 has a domed surface 33. The domed shape of thesurface 33 creates a higher compression zone in the center to promotetissue cutting, while tapering off at the perimeter to promote tissuedessication and adhesion without cutting.

In another embodiment, as illustrated in FIGS. 7c and 8d , a raisedsurface 32 is designed to increase the compression force on the tissuein the center, while creating a wider weld band 21 (FIG. 9) around theperimeter. The wider weld band creates a stronger weld. The width of theraised center section may be adjusted to be narrower or wider in orderto achieve the desired weld strength or anastomosis opening geometry. Asillustrated in FIG. 8e , a slit between the two vessels can be createdby making the raised surface 32 extremely narrow. As the surface area ofthe mating section of the distal heating assembly 4 is decreased, theamount of heat transferred from the active heater will decrease. Thiscan be useful if less heat is needed between two different anatomicalstructures that are being welded. Another feature of a narrow raisedsection is a temperature gradient across the distal heating assembly 4that increases radially from the raised section. A temperature gradientallows the heat to be the highest at the center, which completelydenatures and cuts through tissue, creating an anastomosis. As thetemperature decreases radially, the tissue has less necrosis, yet theproteins are denatured, which leads to a strong weld and long termhealing.

The shape of the distal heating assembly 4, in combination withcompression force, influences the rate at which the passive heatingelement cuts through the tissue. If too much heat or pressure is appliedabruptly, distal heating assembly 4 may quickly cut through the tissuewithout transferring enough heat to the surrounding tissue to achieve asatisfactory weld. Instead, a balance of heat and pressure is requiredto dessicate and denature the protein in the tissue surrounding the cutto promote adhesion prior to cutting. In order to best achieve thisbalance, the temperature and position of the distal tip are monitoredduring the welding process and the heat and/or pressure being applied isadjusted to achieve the desired rate and to ensure that the distalheating assembly 4 and proximal heating assembly 2 are directly opposedto ensure complete weld fusion and aperture cutting. Different heatprofiles may also be designated, based upon the starting tissuethickness prior to joining the tissue. In an embodiment as illustratedin FIG. 4b , heating element 8 is embedded in the conductive proximalheat spreader 12 that is a component of the proximal heating assembly 2for tissue compression. Heating element 8 has a serpentine shape toincrease the surface area in contact with the proximal heat spreader 12to provide more effective heat transfer to the tissue to promotecontrolled dessication and adhesion without cutting through the tissuetoo rapidly.

In another embodiment, as illustrated in FIG. 4c , the active heatingelement within the proximal heating assembly 2 may be configured to haveseparate elliptical elements that provide independent power delivery forheating and cutting. The outer element can be configured to deliverreduced heat to promote controlled dessication and adhesion in the weldzone without cutting through the tissue, while the inner element can beconfigured to deliver increased heat to promote rapid cutting throughthe tissue in the cutting zone.

In a modified embodiment of the intraluminal anastomotic device 1′, asillustrated in FIG. 11b , wherein like elements to those in theembodiment of FIGS. 1a and 1b are denoted by like reference numerals,primed, an active distal heating element 9 is embedded into the distalheat spreader 24′, rather than the passive heat spreader 24 employed inthe FIG. 1 embodiment. This is beneficial if separate heating profilesare required for different tissue types. For example, if joining a thickartery to a vein, it may be beneficial to apply more heat to the thickartery because it dissipates more heat and requires more energy todenature the tissue. Distal heating element 9 may be constructedsimilarly to the heating element 8′ within the proximal heating assembly2′, and may have a closed loop temperature control so that temperaturemay be precisely controlled independently from heating element 8′.Alternatively, the distal heating element 9 can also be heated usingelectrodynamic inductive energy. In this case, a primary coil isintegrated into the proximal heating assembly 2′ and a secondary coil,which can be tuned to the same natural frequency, is embedded in thedistal heating assembly 4′. As the proximal heating assembly 2′ heats,current passes through the primary coil, creating a magnetic field whichacts on the embedded coil in distal heating assembly 4′, creating acurrent that heats the resistive element.

It is important for the proximal and distal heating assemblies 2, 2′ and4, 4′ in both embodiments to have a non-stick surface to preventdenatured tissue from bonding to the device. If tissue bonds to thedevice, the weld between vessels can be damaged or weakened duringremoval of the device. Multiple different coatings or surfacemodifications can be applied to the components to create a non-sticksurface. In one preferred embodiment, components of the device have asurface finish of <16 Ra and are coated using a high temperatureParylene. Other non-stick coatings, such as Poly Tetra Fluoro Ethylene(PTFE), Titanium Nitride (TiN), Chromium Nitride (CrN), Dicronite,silicone, or other similar coatings known to those skilled in the artmay be used to prevent tissue adherence.

In the embodiments of FIGS. 3a and 3b , it is important that an innertube 16 also have a non-stick surface to prevent coagulated blood andtissue from bonding to the surface and obstructing the annular gapbetween the outside diameter of the inner tube 16 and the insidediameter of the proximal heating assembly 2. If blood or tissue bonds toor obstructs this annular gap, this may prevent effective compressiveforce transmission to the distal heating assembly 4 and compromisetissue weld fusion or tissue cutting. In one preferred embodiment, theoutside diameter of the inner tube 16 and inside diameter of theproximal heating assembly 2 1) have a surface finish of <16 Ra, 2) havean annular gap of 0.0005-0.0002 inches, and 3) are coated with a hightemperature non-stick material as previously discussed.

The embodiment illustrated in FIGS. 2a and 2b provides distal tipfeedback, wherein movement of the distal heating assembly 4 is convertedto a signal by a position sensor 36 within the handpiece 6, or,alternatively, outside of the handpiece 6. This movement can then bedisplayed and/or utilized for a control algorithm. A signal that relaysthe absolute position of the distal heating assembly 4 from the positionsensor 36 to a display device (not shown) of some type, through anoutput signal cable 34 is valuable for verifying the tip positionthroughout the procedure and for determining the thickness of the tissuebetween the tip and base of the catheter before, during, and after theformation of the fistula 25 (FIG. 10). The tissue thickness is relatedto the distance measurement by the equation T=d sin θ. The tissuethickness before the procedure can be correlated to the length of thefistula post-procedure. The relative position of the distal heatingassembly 4 during the formation of the fistula 25 is also valuable andcan be related to the rate of tissue dessication, cutting and welding.This signal may be used as an input to control heat application. Forexample, in FIG. 2a , the proximal heating assembly 2 and distal heatingassembly 4 are spaced by a distance d₁, prior to the procedure. Basedupon the type and thickness of the tissue through which the anastomosisis being created, and other factors related to functionality anddurability of the fistula, tip position after the procedure can provideconfirmation that the tissue was properly desiccated and both vesselwalls have been cut. After the procedure, the tip is moved forward to aspaced position d₂ (FIG. 2b ) for device extraction and the position ofthe tip can be verified using the sensor(s) 36.

In FIG. 5, there is illustrated an embodiment of the proximal heatingassembly 2 wherein the heating element 8 is comprised of tungsten, andthat tungsten heating element is sandwiched between two ceramic layers,comprising together the proximal heat spreader 12.

Referring now particularly to FIGS. 9 and 10, a method for using thedevice 1, 1′ will be discussed. To begin the inventive method ofintravascular access and communication, the practitioner selects anappropriate procedural site having each of a primary blood vessel 20 anda secondary blood vessel 22 in close proximity to one another. Incurrently preferred approaches, the primary blood vessel 20 comprises avein, and the secondary blood vessel 22 comprises an artery, but theinvention is not limited to this arrangement. Initially, a piercingdevice is inserted into the primary vessel 20 and actuated to pierce thevessel walls and extend into the adjacent secondary vessel 22. Oncepenetration from primary blood vessel 20 to secondary blood vessel 22has been achieved, the guidewire 17, preferably having a diameter of0.014″ or less, is advanced until the guidewire is positioned in theblood flow path of blood vessel 22 sufficiently to allow the piercingdevice to be removed while retaining the guidewire's position in bloodvessel 22.

Once guidewire 17 is sufficiently in position as previously described,the practitioner withdraws the piercing device completely from the body,thus leaving the guidewire in the desired position and crossing fromprimary vessel 20 to secondary vessel 22. One exemplary piercing systemand methods is disclosed in co-pending U.S. application Ser. No.13/668,190, already expressly incorporated herein by reference, but anysuitable piercing system and method may be used within the scope of thepresent invention.

Now, as disclosed, for example, in a manner similar to those disclosedin prior Provisional U.S. Application Ser. No. 61/596,670, alreadyexpressly incorporated herein by reference, the anastomosis using theembodiments of the present invention may be created. The guidewire 17creates an access path for the device 1, 1′. The device 1, 1′ isinserted into the patient by loading a proximal end of the guidewire 17into the lumen 18 of tip 5. The device 1, 1′ is advanced further intothe patient, tracking over the guidewire 17, until the tapered dilatingdistal tip 5 comes into contact with the selected anastomosis site. Thedevice 1, 1′ can be tracked over the guidewire with the distal tipextended (as shown in FIG. 2a ) or retracted (as shown in FIG. 2b ). Thedistal heating assembly 4 is extended and further advanced into thesecond vessel 22 by advancing the inner tube 16 distally, therebydilating the opening 25 in the vessel, so that the distal tip 5 is inthe second vessel 22, and the proximal base 10 is in the first vessel20, with its heat spreader surface 12 contacting the inner wall of thefirst vessel 20. At this juncture, the opening 25 formed in the adjoinedwalls of vessels 20 and 22 has recovered back to a smaller diameter andfits tightly around the device.

After the distal tip 5 is advanced into the second vessel 22, asillustrated in FIG. 9, a slight tension, or alternatively a slightpressure, is applied to the proximal heat spreader 12 to seat it againstthe vessel wall and promote vessel apposition. The blunt shape of theproximal end 24 of the distal tip 5 prevents the distal tip frominadvertently retracting back through the vessel wall. The proximal end24 of the distal heating assembly 4 is then retracted to close thespacing between the respective proximal and distal heating assemblies,until the walls of the first and second vessels 20 and 22 respectively,are captured between the facing blunt surfaces of each of the proximalheat spreader 12 and the distal heat spreader 24.

A controlled tension is maintained between the distal tip 5 and theproximal base 10, and at this juncture, with the vessels securelyclamped, energy is applied to the proximal heating element 8, as well asto the distal heating element 9 in the case of the modified embodiment1′. As the heat elements weld and cut the vessels, the heat elementswill move closer to one another. When fully retracted, the system isdesigned so that the two heat elements come into direct contact with oneanother to ensure a complete cut and capture of the vessel tissue to beremoved. A variety of DC resistive energy profiles may be used toachieve the desired coaptation and cutting. For example, a rapidlystepped or ramped increase to achieve and maintain a desired temperaturesetting of 150° C.-350° C. may be applied to maximize welding prior tocutting. Energy may be modulated based upon the impedance of the tissueor temperature feedback. Different energy application durations, orcyclic pulses may be used to maximize welding and cutting, whileminimizing heat transfer to adjacent tissues. The distal tip 5 isconfigured to have insulating properties to minimize heat transfer toadjacent tissues and/or fluids. The active heat element is a generallyoval shape and cuts an anastomosis larger that the diameter of theproximal base 10. Within the oval shape of the cutting elements, theremay be provided, if desired, a cavity for capturing the tissue that hasbeen cut. As noted above, the entire surface of the proximal and distalheat elements is configured to have a non-stick coating, such as PTFE,to limit tissue adhesion.

Regarding the tissue welding process, more particularly, the DCresistive energy functions to fuse or weld the vessels together,creating an elongate aperture 25 (FIG. 10) through the opposing walls ofeach of the first and second vessels, as well as any intervening tissue.As formed, the elongate aperture may typically resemble a slit. However,as pressurized flow begins to occur through aperture 25, which creates acommunicating aperture between the first and second blood vessels, theaperture widens in response to the pressure, taking the shape of anellipse as it opens to form the desired fistula. The effect isillustrated in FIG. 10. The edges 21 of the aperture are cauterized andwelded. Outwardly of the weld band 21 is a coaptation area 23. As shown,the cut area corresponds to the shape of the heating or cutting element.It can be of multiple shapes, such as round, oval, a slit, or acombination as shown. The area adjacent to the cut has been approximatedand welded due to the flat face of the catheter in the vein (firstvessel) being larger than the heating surface 12. The heat from theheating surface 12 is also preferably spread over this area by aconductive material that can be above, below or within the heatingsurface 12 or base 10. This creates a temperature gradient, which is aparticularly advantageous feature of the present invention.

Once the fistula 25 has been fully formed, the entire instrument 1, 1′and guidewire 17 are withdrawn.

Other embodiments and approaches are contemplated, but not fullyillustrated herein. For example, in certain applications, it may beadvantageous to provide an outer lumen surrounding the proximal base 10and tapered at the same angle. After the creation of the anastomosis 25,the outer lumen may be advanced until it comes into contact with thewall of the primary vessel 20. With slight forward pressure on the outerlumen, the proximal base and distal tip are retracted into the outerlumen. The outer lumen provides support to the surrounding tissue, andprevents the weld area from being damaged during the removal step. Theouter lumen may be utilized in conjunction with any of the previouslydisclosed embodiments.

In an alternative method, after welding, the distal heating assembly 4may be advanced to separate it and the proximal heating assembly 2.Prior to retracting the distal heating assembly 4 through the fistula25, the distal heating assembly 4 is rotated 45-180 degrees such thatthe taper of the assembly is oriented to create a ramp when beingretracted through the fistula.

In yet another alternative method, the tip can be retracted by keepingthe distal and proximal heating assemblies 4 and 2, respectively,together, applying heat, and applying a retraction force to the device1, 1′. The heat will cause the tissue to expand away from the catheteras it is removed.

Other optional alternative configurations are as follows:

1) External Inductive Activation Energy

An alternative embodiment may be constructed wherein inductiveactivation energy is supplied from outside, or external to, the body anddoes not have a direct electrical connection to the catheter. An emitteris placed in close proximity to the desired fistula location, adjacentto the catheter tip. The activation energy then travels through the skinand surrounding tissue without effect, but creates heat through reactiveelements in the catheter tip and base.

2) Distal Tip Angle

Another alternative embodiment is contemplated wherein the catheter,with cylindrical shape, is comprised of a stationary base with movabletip, wherein the interface between the base and tip have a coplanarinterface, and further wherein the angle ( ) of the interface is between15 and 50 degrees.

3) Expandable Distal Tip

Another alternative embodiment may be provided wherein the distal tip isexpandable to allow for a reduced area profile of the distal tip forentry into and exit from the adjacent vessel and an expanded areaprofile to increase the area of compression for vessel wall welding andcutting. It remains in the closed, or reduced area profile position asthe catheter is advanced to the target site for the anastomosis and thedistal tip enters the artery which limits potential trauma as the distaltip dilates through the vessel wall. Once the catheter is in place atthe target site for the anastomosis, the distal tip is retracted towardthe proximal tip and a compressive counter force from the proximal tipis applied to the rigid spreader faces of the distal tip, which causethem to pivot to the open position and apply a greater surface area ofcompression to the adjacent vessel walls captured between the proximaland distal tip.

Still another embodiment is contemplated wherein the distal tip isexpandable to allow for a reduced area profile of the distal tip forentry into and exit from the adjacent vessel and an expanded areaprofile to increase the area of compression for vessel wall welding andcutting. The distal tip is comprised of a flexible elastomeric materialsuch as silicone, though other materials may be used. In a mannersimilar to the previous embodiment, the catheter is positioned at thetarget site for the anastomosis in the reduced area profile position andthe distal tip is retracted toward the proximal tip and a compressivecounter force from the proximal tip is applied to the elastomericmaterial of the distal tip, which causes the distal tip to expandradially outward and apply a greater surface area of compression to theadjacent vessel walls captured between the proximal and distal tip.

4) Cooling Methods

An approach for cooling the proximal heating assembly 2 near the activeheat element may be desired to prevent unintended heat transfer andnecrosis to adjacent vascular tissue. To achieve this, it is desired tokeep the surface temperature of the catheter components near the activeand passive heat elements below 150 F. An embodiment is contemplatedwherein an inner infusion lumen, which may be auxiliary lumen 15 shownin FIGS. 4 and 5, is employed in the catheter shaft that allows roomtemperature sterile saline to be infused through the inner lumen andexits the proximal tip near the active heat element. In thiscontemplated embodiment, the exit is within 2 mm of the active heatelement, though the position can be up to 10 mm spaced from the activeheat element. In one particular method, the saline flow rate is 3cc/min, though the rate can be variable from 2-5 cc/min.

Another embodiment is contemplated wherein an outer infusion lumen isemployed that allows room temperature sterile saline to be infusedthrough the annular space between the catheter shaft and outer lumen andexit near the active heat element on the proximal tip. The lumen can beincorporated into the vascular access sheath, or can be incorporatedseparately. Like the previous embodiment, the exit is within 2 mm of theactive heat element, though the position can be up to 10 mm away fromthe active heat element. In this method, the saline flow rate is 3cc/min, though the rate can be variable from 2-5 cc/min.

Yet another embodiment utilizes a passive thermal conductive element,which is embedded in the proximal heating assembly 2 and provides a heatsink to shunt unintended heat from the active heat element and theplastic material of the proximal heating assembly 2, conducting itproximally in the catheter. The passive heat conductive element can befabricated of aluminum, copper, stainless steel, ceramics and many otherthermally conductive materials.

Accordingly, although an exemplary embodiment and method according tothe invention have been shown and described, it is to be understood thatall the terms used herein are descriptive rather than limiting, and thatmany changes, modifications, and substitutions may be made by one havingordinary skill in the art without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A device for creating an arteriovenous (AV)fistula, comprising: a proximal base having a distal tapered endsurface; a distal tip connected to the proximal base and movablerelative to the proximal base, said distal tip having a proximal taperedend surface; a first heating assembly comprising an energized heatingelement disposed on one of said distal tapered end surface or saidproximal tapered end surface; and a second heating assembly comprising apassive non-energized heat spreader disposed on another one of saiddistal tapered end surface or said proximal tapered end surface; whereinthe distal tapered end surface and the proximal tapered end surface areadapted to contact opposing sides of a tissue portion to create the AVfistula; and wherein the passive non-energized heat spreader comprises aplurality of raised segments forming a segmented rib for creating afocused heat conduction path through the tissue portion.
 2. The deviceas recited in claim 1, wherein said distal tapered end surface isoriented at an angle of 15-90 degrees relative to a longitudinal axis ofsaid device.
 3. The device as recited in claim 2, wherein said distaltapered end surface is oriented at an angle of 15-50 degrees relative tosaid longitudinal axis.
 4. The device as recited in claim 3, whereinsaid distal tapered end surface is oriented at an angle of approximately23 degrees relative to said longitudinal axis.
 5. The device as recitedin claim 1, wherein a taper of said proximal tapered end surface matchesa taper of said distal tapered end surface, so that the distal andproximal tapered end surfaces match one another and fully engage withone another when engaged.
 6. The device as recited in claim 1, andfurther comprising a shaft for connecting the distal tip to the proximalbase, the shaft being extendable and retractable to extend and retractsaid distal tip relative to the proximal base.
 7. The device as recitedin claim 6, wherein each of the first and second heating assembliescomprise non-stick surfaces.
 8. The device as recited in claim 7,wherein the shaft also comprises a non-stick surface.
 9. The device asrecited in claim 8, wherein the non-stick surfaces of the first andsecond heating assemblies and the shaft have a surface finish of lessthan 16 Ra.
 10. The device as recited in claim 1, wherein the one ofsaid distal tapered end surface or said proximal tapered end surface onwhich the first heating assembly is disposed has a second passivenon-energized heat spreader disposed thereon.
 11. The device as recitedin claim 10, wherein the passive non-energized heat spreader comprises athermally conductive material which extends across a substantial portionof the one of said distal tapered end surface or said proximal taperedend surface on which it is disposed, the passive non-energized heatspreader being in thermal contact with the energized heating element todraw heat from the energized heating element and spread the heat acrossthe respective distal or proximal tapered end surface.
 12. The device asrecited in claim 11, wherein the passive non-energized heat spreader isconstructed so that it has a thickness approximately equal to athickness of a vessel in which the device is deployed, said thicknessfalling within a range of 0.010 inches to 0.060 inches.
 13. The deviceas recited in claim 1, wherein the energized heating element comprises aserpentine configuration.
 14. The device as recited in claim 1, andfurther comprising a temperature sensor near the energized heatingelement for providing closed loop temperature control to the firstheating assembly.
 15. The device as recited in claim 1, wherein thedistal tip comprises a tapered outer surface, tapering down from theproximal tapered end surface toward a distal end thereof, the distal endof the distal tip comprising an aperture for a through lumen forreceiving a guidewire, wherein a width of the distal tip at the lumenaperture is approximately equal to a diameter of the guidewire.
 16. Thedevice as recited in claim 1, wherein the energized heating elementcomprises separate elliptical elements that provide independent powerdelivery for heating and cutting.
 17. The device as recited in claim 16,wherein the separate elliptical elements comprise an outer element andan inner element, the outer element being configured to deliver reducedheat to promote controlled desiccation and adhesion in a weld zonewithout cutting through tissue and the inner element being configured todeliver increased heat to promote rapid cutting through tissue in acutting zone.
 18. The device as recited in claim 1, wherein the firstheating assembly is disposed on the distal tapered end surface and thesecond heating assembly is disposed on the proximal tapered end surface.19. The device as recited in claim 18, and further comprising a secondactive energized heating element on the proximal tapered end surface.20. The device as recited in claim 19, wherein the second activeenergized heating element is embedded into the passive non-energizedheat spreader.
 21. The device as recited in claim 1, and furthercomprising a position sensor for monitoring movement of the distal tip.22. The device as recited in claim 1, wherein the segmented rib furthercomprises gaps between the plurality of raised segments, said gapsproviding an insulative barrier that limits tissue desiccation topromote adhesion without cutting.